Recently, a PRAM (Phase-change Random Access Memory) that stores thereon information by using a phase-change film is attracting attention as a high-speed nonvolatile memory device having a long lifetime.
A phase of a phase-change film is changed between an amorphous phase and a crystalline phase through, for example, a temperature variation. The PRAM stores data by using a difference between resistance values of these two phases. A driving force for the phase change may be obtained by, for example, controlling a pulse amplitude of an electric current.
Ge2Sb2Te5, which is a Ge—Sb—Te film, is used as a material for the phase-change film in the PRAM. Conventionally, the Ge—Sb—Te film has been generally formed by PVD such as sputtering. However, since a sufficient step coverage cannot be achieved by PVD, it has been attempted in, for example, Patent Document 1 to form a Ge—Sb—Te film by ALD or CVD which enables obtaining the sufficient step coverage.                Patent Document 1: Japanese Patent Laid-open Publication No. 2009-274949        
In Patent Document 1, however, composition controllability as a process is not high, and a composition of the obtained Ge—Sb—Te film is mostly GeSb4Te7. Further, the Ge—Sb—Te film formed by the method of Patent Document 1 has problems such as low surface smoothness and poor electrical characteristics (for example, a duration in which a high resistance state is maintained is short).